97
CHAPTER 6 CLOCK GENERATOR
6.6.2 Switching CPU clock
The following figure illustrates how the CPU clock switches.
Figure 6-6. Switching CPU Clock
V
DD
RESET
CPU clock
Slowest
operation
Fastest
operation
Wait (15.6 ms: at 8.38-MHz operation)
Internal reset operation
<1> The CPU is reset when the RESET pin is made low on power application. The effect of resetting is released
when the RESET pin is later made high, and the main system clock starts oscillating. At this time, the time
during which oscillation stabilizes (2
17
/f
X
) is automatically secured.
After that, the CPU starts instruction execution at the slowest speed of the main system clock (3.81
µ
s: at
8.38-MHz operation).
<2> After the time during which the V
DD
voltage rises to the level at which the CPU can operate at the highest
speed has elapsed, PCC is rewritten so that the highest speed can be selected.
Содержание mPD780973 Series
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